2FA Codes (TOTP)

ZeroKeyUSB can generate TOTP codes (RFC 6238) fully offline — the same ones you’d see in Google Authenticator, without a phone. This guide covers the usage flow. To add a TOTP secret to a credential, see Importing credentials.

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Step 1 — Navigate to the 2FA field

From the credential’s main screen, press Down until you reach the 2FA field. The icon switches from padlock (Pass) to key (2FA). If the credential has a secret loaded, you’ll see 2FA (OK). Otherwise, 2FA --. With the 2FA field selected (inverted key icon), press Center (short) to start calculating the code.

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Step 2 — Enter the date (first time per session)

The ATECC608A has no RTC. It needs date and time just once per session (between power cycles). The device asks for the date first in DD/MM/YY format. Set today’s date and press Center.

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Step 3 — Enter the time

Same flow, now in HH:MM (24h local time) format. Same buttons as the date. When done, press Center to compute the code.

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Step 4 — View the TOTP code

After entering date and time, the ATECC608A computes HMAC-SHA1 of secret + epoch/30 and shows the resulting 6 digits. The bottom bar empties as the 30-second window approaches its end. With your cursor on the 2FA input field of your app, short-press Center. The device types the 6 code digits to the host as if from a normal keyboard.

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Step 5 — Subsequent codes in the same session

While the device stays plugged in, you won’t have to re-enter date and time. The next time you enter a 2FA field (in any credential), you jump straight to step 4 with a code computed using the current time. Short-press Center to type the code to the host, or Left to return to the credential’s main view without typing anything.

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Quick reference

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Next steps